Memory system, memory module and method to backup and restore system using command address latency

ABSTRACT

A memory system having a plurality of memory devices includes a controller for separately accessing the memory devices. The memory system includes a data bus for transferring data, a control bus for transferring a command and address CAL, and first and second memory devices coupled to the data bus and the control bus. The controller controls the first and second memory devices through the data bus and the control bus, wherein the first and second memory devices have different values of the CAL, and wherein a difference of the CAL values is greater than or equal to a RAS to CAS delay time tRCD.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application No.10-2015-0052427, filed on Apr. 14, 2015, which is incorporated herein byreference in its entirety.

BACKGROUND

1. Field

This patent document relates to a memory system and a memory module.

2. Description of the Related Art

In most cases, a single controller is used to control multiple memorydevices.

As illustrated in FIG. 1A, when a control bus CMD/ADDR_BUS0 and a databus DATA_BUS 0 between a controller 100 and a memory device 110_0 areseparated from a control bus CMD/ADD_BUS1 and a data bus DATA_BUS1between the controller 100 and a memory device 110_1, the controller 100can separately control the memory devices 110_0 and 110_1. A command andaddress are transmitted through the control bus. For example, while thememory device 110_0 performs a read operation, the memory device 110_1may perform a write operation.

As illustrated in FIG. 1B, when a control bus CMD/ADDR_BUS and a databus DATA_BUS are shared by the memory devices 110_0 and 110_1, lines fortransmitting signals CS0 and CS1 for distinguishing between the memorydevices 110_0 and 110_1 are provided. The lines for transmitting thesignals CS0 and CS1 among signals of the control bus CMD/ADDR_BUS areseparately provided for the respective memory devices 110_0 and 110_1.In this case, a memory device selected by the signals CS0 and CS1between the memory devices 110_0 and 110_1 may perform an operation inresponse to the command transferred through the control busCMD/ADDR_BUS, and exchange signals with the controller 100 through thedata bus DATA_BUS. The signals CS0 and CS1 are command signalstransmitted to the control bus CMD/ADD_BUS, but are independentlyallocated to the memory devices 110_0 and 110_1 unlike the other commoncommand signals transmitted through the control bus CMD/ADDR_BUS. Thus,the signals CS0 and CS1 are separately illustrated in FIG. 1B.

As the number of memory devices coupled to the controller increases, thenumber of lines required increases. This lead to increase difficultiesin system design as well as increased manufacturing costs.

SUMMARY

Various embodiments are directed to a memory system which includes acontroller capable of separately accessing memory devices, whilereducing the number of lines between the controller and memory devices.

In an embodiment, a memory system may include: a data bus suitable fortransferring data; a control bus suitable for transferring commands andaddresses including a command address latency (CAL); first and secondmemory devices commonly coupled to the data bus and the control bus; anda controller suitable for controlling the first and second memorydevices through the data bus and the control bus, wherein the first andsecond memory devices have different values of the CAL, and wherein adifference of the CAL values is greater than or equal to a RAS to CASdelay time (tRCD).

The difference of the CAL values is smaller than a row precharge time(tRP).

In an embodiment, a memory module may include: a first data bus suitablefor transferring data; a control bus suitable for transferring commandsand addresses including a command address latency (CAL); a plurality offirst volatile memory devices commonly coupled to the first data bus andthe control bus; one or more nonvolatile memory devices; and acontroller suitable for providing the commands and addresses through thecontrol bus and the first data bus to store data of the plurality offirst volatile memory devices into the nonvolatile memory devices when atrigger condition is satisfied, wherein when the trigger condition issatisfied, the controller controls a specific one of the plurality offirst volatile memory devices to have the CAL of a first value, and theothers of the plurality of first volatile memory devices to have the CALof a second value.

The commands and addresses may include the CLA of the first value whenthe controller accesses the specific one of the plurality first volatilememory devices.

The memory system may further include: a second data bus suitable fortransferring data; and a plurality of second nonvolatile memory devicescommonly coupled to the second data bus and the control bus, wherein thecontroller further provides the command and address through the controlbus and the second data bus to store data of the plurality of secondvolatile memory devices into the nonvolatile memory devices, when thetrigger condition is satisfied, and wherein when the trigger conditionis satisfied, the controller controls a specific one of the plurality ofsecond volatile memory devices to have the CAL of the first value, andthe others of the plurality of second volatile memory devices to havethe CAL of a second value.

The command and address may include the CAL of the first value when thecontroller accesses the specific one of the plurality of second volatilememory devices.

In an embodiment, there is provided an operation method of a memorymodule including first to Nth volatile memory groups, each of whichincludes one or more volatile memory devices, one or more nonvolatilememory devices, and a controller. The operation method may include:exchanging data between the first to Nth volatile memory groups and amemory controller of a host; controlling, by the controller, a specificone of the first to Nth volatile memory groups to have a command addresslatency (CAL) of a first value, and the others of the first to Nthvolatile memory groups to have the CAL of a second value when a triggercondition is satisfied; and providing commands and addresses includingthe CAL of the first value to store data of the specific one of thefirst to Nth volatile memory groups into the nonvolatile memory deviceswhen the trigger condition is satisfied.

The operation method may further include: controlling, by thecontroller, the specific one of the first to Nth volatile memory groupsto have the CAL of a third value, and the others of the first to Nthvolatile memory groups to have the CAL of a fourth value when arestoration condition is satisfied; and providing commands and addressesincluding the CAL of the third value to restore data of the nonvolatilememory devices into the specific one of the first to Nth volatile memorygroups when the restoration condition is satisfied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating bus coupling between a controller andmemory devices in a conventional memory system.

FIG. 2 is a timing diagram illustrating an operation according to a MRSduring a PDA mode in a memory device.

FIG. 3 is a diagram illustrating command address latency CAL of a memorydevice.

FIG. 4 is a block diagram illustrating a memory system in accordancewith an embodiment of the present invention.

FIG. 5 is a flowchart illustrating an operation of the memory system ofFIG. 4.

FIG. 6 is a timing diagram illustrating steps 512 and 513 of FIG. 5.

FIG. 7 is timing diagrams illustrating steps 521 and 522 of FIG. 5.

FIG. 8 is a diagram illustrating a CAL difference (dCAL) between memorydevices, a RAS to CAS delay time (tRCD) and a row precharge time (tRP).

FIG. 9 is a block diagram illustrating a memory module in accordancewith an embodiment of the present invention.

FIG. 10 is a flowchart illustrating an operation of the memory moduleillustrated in FIG. 9.

FIG. 11 is a block diagram illustrating a memory module in accordancewith another embodiment of the present invention.

DETAILED DESCRIPTION

Various embodiments will be described below in more detail withreference to the accompanying drawings. The present invention may,however, be embodied in different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the present invention to those skilled inthe art. Throughout the disclosure, like reference numerals refer tolike parts throughout the various figures and embodiments of the presentinvention.

Before embodiments of the present invention are described, a Per DRAMAddressability (PDA) mode and Command Address Latency (CAL) of a memorydevice will be described as follows.

FIG. 2 is a timing diagram illustrating an operation according to a moderegister set (MRS) during the PDA mode in a memory device.

During the PDA mode, memory devices may be enabled to performindependent MRS operations. When the PDA mode is set, the validities ofall MRS commands can be determined according to the signal level of azeroth data pad DQ0. When the signal level of the zeroth data pad DQ0 is‘0’ after the write latency WL, which is sum of the Additive Latency(AL) and the CAS Write Latency (CWL) from the time point at which a MRScommand is applied, the applied MRS set command may be determined to bevalid. When the signal level of the zeroth data pad DQ0 is ‘1’ after thewrite latency WL from the time point at which the MRS command isapplied, the applied MRS command may be determined to be invalid andthen ignored.

Referring to FIG. 2, the MRS command MRS may be applied to a memorydevice at a time point 201. At a time point 202 or the write latency(WL=AL+CWL) after the time point 201, the signal level of the zerothdata pad DQ0 may transition to ‘0’ during a predetermined period. Thus,the MRS command MRS applied at the time point 201 may be determined tobe valid, and a setting operation of the memory device using an address(not illustrated) inputted with the MRS command may be performed duringa MRS command cycle time tMRD_PDA from a time point 203.

When the signal level of the zeroth data pad DQ0 is continuouslyretained as ‘1’ at the time point 202, the MRS command MRS applied atthe time point 201 may be determined to be invalid and ignored. That is,a setting operation of the memory device may not be performed.

FIG. 3 is a diagram illustrating the CAL of the memory device.

The CAL indicates a timing difference between a chip select signal andthe other control signals of the control signals transmitted to thecontrol bus CMD/ADDR_BUS. When the CAL is set, the memory device maytake valid control signals, which are inputted the CAL after theenablement of the chip select signal CS. The value of the CAL may be setby the MRS.

FIG. 3 illustrates an operation when the CAL is set to three clockcycles. The chip select signal CS may be low-enabled at time points 301and 305. At a time point 302 where three clocks have elapsed from thetime point 301, the command CMD, except for the chip select signal CS,and address ADDR may be applied to the memory device. Then, the memorydevice may recognize that the command CMD and address ADDR applied atthe time point 302 are valid. Although the command CMD and address ADDare applied to the memory device at the same time point as the timepoint 301 or at a time point where one or two clocks have elapsed fromthe time point 301, the memory device may recognize that the command CMDand address ADD are invalid.

Since the command CMD and address ADDR are applied at time points 304and 306 or the three clocks of the CAL after the time points 303 and305, the memory device may recognize that the command CMD and addressADDR applied at the time points 304 and 306 are valid.

FIG. 4 is a block diagram illustrating a memory system in accordancewith an embodiment of the present invention.

Referring to FIG. 4, the memory system may include a controller 400, afirst memory device 410_0, a second memory device 410_1, a control busCMD/ADDR_BUS, and a data bus DATA_BUS.

Through the control bus CMD/ADDR_BUS, the control signals may betransmitted to the memory devices 410_0 and 410_1 from the controller400. The control signals may include the command CMD, an address ADDR,and a clock CK. The command CMD may include a plurality of signals. Forexample, the command may include an active command ACT, a row addressstrobe signal RAS, a column address strobe signal CAS, and the chipselect signal CS. Although the chip select signal CS is included in thecommand CMD, FIG. 4 separately illustrates the chip select signal CS inorder to indicate that the memory devices 410_0 and 410_1 share the samechip select signal CS. The address ADDR may include a plurality ofsignals. For example, the address ADDR may include a multi-bit bankgroup address, a multi-bit bank address, and a multi-bit normal address.For a synchronized operation of the memory devices, the clock CK may betransmitted to the memory devices 410_0 and 410_1 from the controller400. The clock CK may be transmitted through a differential methodincluding a main clock CK_t and a sub clock CK_c obtained by invertingthe main clock CK_t.

The data bus DATA_BUS may transfer multi-bit data DATA0 to DATA3 betweenthe controller 400 and the memory devices 410_0 and 410_1. Each of thememory devices 410_0 and 410_1 may include data pads DQ0 to DQ3 coupledto data lines DATA0 to DATA3 of the data bus DATA_BUS. The memorydevices 410_0 and 410_1 may share the data bus DATA_BUS, but may becoupled to the data bus DATA_BUS with different data pads DQ0 to DQ3.For example, data pads DQ0 among the data pads DQ0 to DQ3 of the memorydevices 410_0 and 410_1 may be coupled to different data lines DATA0 andDATA1, respectively. The specific data pad DQ0 may be used to setlatency for recognizing the control signals of the control busCMD/ADDR_BUS.

The controller 400 may control the memory devices 410_0 and 410_1through the control bus CMD/ADDR_BUS, and exchange data with the memorydevices 410_0 and 410_1 through the data bus DATA_BUS. The controller400 may be included in a processor such as a Central Processing Unit(CPU), a Graphic Processing Unit (GPU), or an Application Processor(AP), or exist on a memory module such as a Dual In-line Memory Module(DIMM). Furthermore, the controller 400 may exist in various types. Forexample, the controller 400 may exist on a separate chip in a systemincluding a memory device (for example, a computing device or mobilephone). The controller 400 may set latencies having various values atwhich the memory devices 410_0 and 410_1 recognize signals on thecontrol bus CMD/ADDR_BUS. Then, the controller 400 may access a desiredmemory device between the memory devices 410_0 and 410_1 using thelatencies. This operation will be described in detail with reference toFIGS. 5 to 7.

The first and second memory devices 410_0 and 410_1 may share thecontrol bus CMD/ADDR_BUS and the data bus DATA_BUS. The first and secondmemory devices 410_0 and 410_1 may also share the line for the chipselect signal CS. The first and second memory devices 410_0 and 410_1may have different latencies to control signals transmitted through thecontrol bus CMD/ADDR_BUS. The latency may indicate a timing differencebetween the chip select signal CS and the other signals CMD and ADDR ofsignals of the control bus CMD/ADDR_BUS. As different latencies are setfor the control bus CMD/ADDR, the first and second memory devices 410_0and 410_1 can be individually accessed by the controller 400. Thisoperation will be described in detail with reference to FIGS. 5 to 7.

As illustrated in FIG. 4, separate signal transmission lines for each ofthe first and second memory devices 410_0 and 410_1 may not be allocatedto the first and second memory devices 410_0 and 410_1 while thecontroller 400 can separately access the first and second memory devices410_0 and 410_1. Hereafter, this operation will be described.

FIG. 5 is a flowchart illustrating the operation of the memory systemdescribed with reference to FIG. 4.

Referring to FIG. 5, the operation of the memory system may include anoperation 510 in which the controller 400 differently sets the latenciesfor the control signals transmitted through the control bus CMD/ADDR_BUSof the first and second memory devices 410_0 and 410_1, and an operation520 in which the controller 400 separately accesses the first and secondmemory devices 410_0 and 410_1. The operation 510 may include steps 511to 514, and the operation 520 may include steps 521 and 522.

At step 511, the controller 400 may control the first and second memorydevices 410_0 and 410_1 to enter the PDA mode by applying a command CMDcorresponding to MRS and by applying an address ADDR corresponding tothe entry of the PDA mode.

At step 512, the controller 400 may set the command address latency(CAL), which corresponds to the control bus CMD/ADDR_BUS of the firstmemory device 410_0, to ‘0’ for example by applying the command CMDcorresponding to MRS, by applying the address ADDR corresponding to theCAL set to ‘0’, and by applying a signal of the zeroth data line DATA0corresponding to the zeroth data pad DQ0 of the first memory device410_0. The signal of the zeroth data line DATA0 may have a level of ‘0’the write latency (WL=AL+CWL) after the time point at which the commandCMD is applied. Referring to FIG. 6, the command/address CMD/ADDR forsetting the CAL to a level of ‘0’ may be set at a time point 601, andthe data line DATA0 may have a level of ‘0’ at a time point 602 wherethe write latency WL has elapsed from the time point 601. Since the dataline DATA1 has a level of ‘1’ at the time point 602, the second memorydevice 410_1 may ignore the command applied at the time point 601.

At step 513, the latency corresponding to the control bus CMD/ADDR_BUSof the second memory device 410_1, that is, the CAL may be set to ‘3’ byapplying the command CMD corresponding to MRS, by applying the addressADDR corresponding to CAL set to ‘3’, and by and applying a signal ofthe first data line DATA1 corresponding to the zeroth data pad DQ0 ofthe second memory device 410_1. The signal of the first data line DATA1may have a level of ‘0’ the write latency (WL=AL+CWL) after the timepoint at which the command CMD is applied. Referring to FIG. 6, thecommand/address CMD/ADDR for setting the CAL to a level ‘3’ may be setat a time point 603, and the data line DATA1 may have a level of ‘0’ ata time point 604 where the write latency WL has elapsed from the timepoint 603. Since the data line DATA0 has a level of ‘1’ at the timepoint 604, the first memory device 410_0 may ignore the command appliedat the time point 603. When the latency settings of the memory devices410_0 and 410_1 are completed, the PDA mode may end at step 514.

Since the CALs of the first and second memory devices 410_0 and 410_1are differently set, the controller 400 may access the first memorydevice 410_0 by applying the command/address CMD/ADDR at the enablementof the chip select signal CS at step 521, and access the second memorydevice 410_1 by applying the command/address CMD/ADDR after three clocksfrom the enablement of the chip select signal CS, at step 522.

FIG. 7 shows timing diagrams illustrating steps 521 and 522 describedwith reference to FIG. 5. Referring to FIG. 7, the first memory device410_0 may receive the commands applied at the time points 701, 703, 705,707, 709, and 711, which is the same as the enablement time points ofthe chip select signal CS, and may start to operate. Furthermore, thesecond memory device 410_1 may receive the commands applied at timepoints 702, 704, 706, 708, 710, and 712 three clocks after theenablement time points of the chip select signal CS, and may start tooperate. In FIG. 7, NOP represents a non-operation state in which nooperation is ordered. At the time points 701, 702, 703, 704, 707, 708,709, and 710, the controller 400 may access one of the first and secondmemory devices 410_0 and 410_1. However, at the time points 705, 706,711, and 712, the controller 400 may access both of the first and secondmemory devices 410_0 and 410_1 by applying a valid command CMD at theenablement of the chip select signal CS and applying a valid command CMDat three clocks after the enablement of the chip select signal CS.

In accordance with the embodiment, the memory devices 410_0 and 410_1may share the control bus CMD/ADDR_BUS and the data bus DAT_BUS, buthave different latencies for the control bus CMD/ADDR_BUS. Furthermore,the controller 400 may access one of the memory devices 410_0 and 410_1by changing latencies of signals applied to the control busCMD/ADDR_BUS. Thus, any further lines need not be added in order toindividually control the memory devices 410_0 and 410_1.

In the above-described embodiment, it has been described that thecontroller 400 controls the memory devices 410_0 and 410_1 to havedifferent latencies for the control bus CMD/ADDR_BUS, but this is onlyan example. The memory devices 410_0 and 410_1 may be programmed topermanently have different latencies. For example, when the memorydevices 410_0 and 410_1 are fabricated, latencies for the control busCMD/ADDR_BUS may be set. Alternatively, after the memory devices 410_0and 410_1 are fabricated, latencies of the memory devices 410_0 and410_1 for the control bus CMD/ADDR_BUS may be permanently set through afuse circuit.

A difference in the CAL between the memory devices 410_0 and 410_1 maybe greater than or equal to a RAS to CAS delay time (tRCD). Furthermore,the difference in the CAL between the memory devices 410_0 and 410_1 maybe less than a row precharge time (tRP). That is, the following relationmay be established: CAL difference dCAL≧tRCD and dCAL<tRP. FIG. 8 is adiagram illustrating the CAL difference (dCAL) between the first andsecond memory devices 410_0 and 410_1, the RAS to CAS delay time (tRCD)and the row precharge time (tRP). In FIG. 8, suppose that the CALdifference (dCAL) of the memory device 410_0 is set to 0, the CAL of thememory device 410_1 is set to 3, CAL difference (dCAL) is set to 3, theRAS to CAS delay time (tRCD) is set to 3, and the row precharge time(tRP) is set to 4.

Referring to FIG. 8, the chip select signal CS may be enabled, and anactive command ACT may be transferred through the command/addressCMD/ADDR at a time point 801. Then, the memory device 410_0 may performan active operation in response to the active command ACT at the timepoint 801.

At a time point 802, the chip select signal CS may be enabled, and aread command RD may be transferred through the command/address CMD/ADDR.Then, the memory device 410_0 may perform a read operation in responseto the read command RD at the time point 802. Furthermore, the memorydevice 410_1 may recognize the read command RD of the command/addressCMD/ADDR at the time point 802, which is three clocks after theenablement time point 801 of the chip select signal CS. However, sincethe memory device 410_1 has never performed the active operation, thememory device 410_1 may void the read command RD ordered through thecommand/address CMD/ADDR without performing the read operation. When theCAL different dCAL is smaller than the RAS to CAS delay time tRCD, amalfunction may occur. For example, the memory device 410_1 mayrecognize the active command ACT ordered for the memory device 410_0.However, when the CAL difference dCAL is greater than or equal to theRAS to CAS delay time tRCD, such a malfunction may be prevented.Furthermore, the memory device 410_1 may recognize the read command RDof the command/address CMD/ADDR at a time point 803, which is threeclocks after the enablement time point 802 of the chip select signal CS.However, since the memory device 410_1 has never performed the activeoperation, the memory device 410_1 may void the read command RD orderedthrough the command/address CMD/ADDR without performing the readoperation.

At a time point 804, the chip select signal CS may be enabled, and theprecharge command PCG may be ordered through the command/addressCMD/ADDR. Then, the memory device 410_0 may perform the prechargeoperation in response to the precharge command PCG at the time point804. Furthermore, the memory device 410_1 may recognize the prechargecommand PCG of the command/address CMD/ADDR, and perform the prechargeoperation at a time point 805, which is three clocks after theenablement time point 804 of the chip select signal CS. The prechargeoperation may be performed regardless of whether the previous activeoperation was performed. Thus, the memory device 410_1 can also performthe precharge operation.

At a time point 806, the chip select signal CS may be enabled, and anactive command ACT may be ordered through the command/address CMD/ADDR.Then, the memory device 410_0 may perform an active operation inresponse to the active command ACT at the time point 806. When the CALdifference dCAL is set to be greater than tRP, a malfunction may occur.For example, the memory device 410_1 may perform an active operation inresponse to the active command ACT ordered through the command/addressCMD/ADD from the time point 806. However, since the CAL difference dCALis smaller than the row precharge time tRP, such a malfunction may beprevented.

At a time point 807, the chip select signal CS may be enabled, and awrite command WT may be ordered through the command/address CMD/ADDR.Then, the memory device 410_0 may perform a write operation in responseto the write command WT at the time point 807. Furthermore, the memorydevice 410_1 may recognize the write command WT of the command/addressCMD/ADDR at the time point 807, which is three clocks after theenablement time point 806 of the chip select signal CS. However, sincethe memory device 410_1 has never performed an active operation, thememory device 410_1 may void the write command WT ordered through thecommand/address CMD/ADDR as illegal without performing the writeoperation. Furthermore, the memory device 410_1 may recognize the writecommand WT of the command/address CMD/ADDR at a time point 808, which isthree clocks after the enablement time point 807 of the chip selectsignal CS. However, the memory device 410_1 may void the write commandWT ordered through the command/address CMD/ADDR without performing thewrite operation.

As described with reference to FIG. 8, the CALs of the memory devices410_0 and 410_1 may be set to satisfy the relation of dCAL tRCD anddCAL<tRP, which makes it possible to prevent malfunctions of the memorydevices 410_0 and 410_1.

FIG. 9 is a block diagram illustrating a memory module 900 in accordancewith an embodiment of the present invention. FIG. 9 illustrates anexample in which the scheme for separately accessing memory devicessharing a data bus and a control bus by differently setting CALs of thememory devices is applied to the memory module 900. FIG. 9 illustrates amemory controller 9 and an emergent power supply unit 10 in addition tothe memory module 900. The memory module 900 may include an NVDIMM (NonVolatile Dual In Line Memory Module). The NVDIMM may back up data ofvolatile memory devices when power of a host is unstable, therebypreventing data loss during power failure.

Referring to FIG. 9, the memory module 900 may include a plurality offirst volatile memory devices 911 to 914, a plurality of second volatilememory devices 921 to 924, a nonvolatile memory device 930, a controller940, a register 950, a power fail detector 960, a first data busDATA_BUS1, a second data bus DATA_BUS2, a control bus CMD/ADDR_BUS, aplurality of third data buses DATA_BAS3_1 to DATA_BUS3_4, and aplurality of fourth data buses DATA_BUS4_1 to DATA_BUS4_4.

When host power HOST_VDD and HOST_VSS is normal, the register 950 maybuffer a command, address, and a clock provided from the memorycontroller 9 of the host through a host control bus HOST_CMD/ADDR_BUS,and provide the buffered command, address, and clock to the firstvolatile memory devices 911 to 914 and the second volatile memorydevices 921 to 924 through the control bus CMD/ADDR_BUS. When the hostpower HOST_VDD and HOST_VSS is normal, the first volatile memory devices911 to 914 may exchange data with the memory controller 9 of the hostthrough corresponding third data buses among the third data busesDATA_BUS3_1 to DATA_BUS3_4, and the second volatile memory devices 921to 924 may exchange data with the memory controller 9 of the hostthrough corresponding fourth data buses among the fourth data busesDATA_BUS4_1 to DATA_BUS4_4. That is, when the host power HOST_VDD andHOST_VSS is normal, the first volatile memory devices 911 to 914 and thesecond volatile memory devices 921 to 924 may communicate with thememory controller 9 of the host through corresponding data buses amongthe third data buses DATA_BUS3_1 to DATA_BUS3_4 and the fourth databuses DATA_BUS4_1 to DATA_BUS4_4.

When detecting a failure of the host power HOST_VDD and HOST_VSS or itis detected that the levels of voltages forming the host power HOST_VDDand HOST_VSS are destabilized, the power fail detector 960 may cut offthe supply of the host power HOST_VDD and HOST_VSS, and operate thememory module 900 using emergent power EMG_VDD and MEG_VSS of theemergent power supply unit 10. The emergent power supply unit 10 may beimplemented with a capacitor having a large capacitance, for example, asuper cap. The emergent power supply unit 10 may supply the emergentpower EMG_VDD and EMG_VSS while data of the first volatile memorydevices 911 to 914 and the second volatile memory devices 921 to 924 arebacked up into the nonvolatile memory device 930. FIG. 9 exemplarilyillustrates that the emergent power supply unit 10 is provided outsidethe memory module 900. However, the emergent power supply unit 10 may beprovided in the memory module 900. When detecting a failure of the hostpower HOST_VDD and HOST_VSS, the power fail detector 960 may notify thecontroller 940 of the failure.

When the failure of the host power HOST_VDD and HOST_VSS is notifiedfrom the power fail detector 960, the control for the first volatilememory devices 911 to 914 and the second volatile memory devices 921 to924 may be switched to the controller 940 from the memory controller 9of the host. The register 950 may buffer the command, address, and clockprovided from the controller 940 in place of the memory controller 9 ofthe host, and may provide the buffered command, address, and clock tothe first volatile memory devices 911 to 914 and the second volatilememory devices 921 to 924 through the control bus CMD/ADDR_BUS. Thefirst volatile memory devices 911 to 914 may exchange data with thecontroller 940 through the first data bus DATA_BUS1, and the secondvolatile memory devices 921 to 924 may exchange data with the controller940 through the second data bus DATA_BUS2. The controller 940 may readthe data of the first volatile memory devices 911 to 914 and the secondvolatile memory devices 921 to 924 through the control bus CMD/ADDR_BUS,the first data bus DATA_BUS1, and the second data bus DATA_BUS2, andback up the read data into the nonvolatile memory device 930.

The data of the first volatile memory devices 911 to 914 and the secondvolatile memory devices 921 to 924, which are backed up into thenonvolatile memory device 930 when a failure of the host power HOST_ADDand HOST_VSS occurs, may be transmitted to the first volatile memorydevices 911 to 914 and the second volatile memory devices 921 to 924after the host power HOST_VDD and HOST_VSS is restored. Such arestoration operation may be performed according to the control of thecontroller 940. After the restoration operation is completed, thecontrol for the first volatile memory devices 911 to 914 and the secondvolatile memory devices 921 to 924 may be switched to the memorycontroller 9 of the host from the controller 940.

Between the controller 940 and the first volatile memory devices 911 to914, there is provided only the control bus CMD/ADDR_BUS and the firstdata bus DATA_BUS1. That is, the first volatile memory devices 911 to914 may share the same control bus and data bus for communication withthe controller 940. Similarly, between the controller 940 and the secondvolatile memory devices 921 to 924, there is provided only the controlbus CMD/ADDR_BUS and the second data bus DATA_BUS2. That is, the secondvolatile memory devices 921 to 924 may share the same control bus anddata bus for communication with the controller 940. However, thecontroller 940 can independently access the first volatile memorydevices 911 to 914, and independently access the second volatile memorydevices 921 to 924. This operation will be described in detail withreference to FIG. 10.

The first volatile memory devices 911 to 914 and the second volatilememory devices 921 to 924 may include DRAM or different types ofvolatile memory devices. The nonvolatile memory device 930 may includeNAND FLASH. However, the nonvolatile memory device 930 is not limitedthereto, but may include all types of nonvolatile memory devices, forexample, NOR FLASH, Resistive RAM (RRAM), Phase RAM (PRAM), Magnetic RAM(MRAM), or Spin Transfer Torque MRAM (STT-MRAM).

The components within the memory module 900 illustrated in FIG. 9 may beintegrated with each other or separated from each other. For example,the controller 940, the register 950, and the power fail detector 960may be implemented as a single chip or implemented as a plurality ofchips. The number of first volatile memory devices 911 to 914, secondvolatile memory devices 921 to 924, and the nonvolatile memory device930 included in the memory module 900 may vary.

FIG. 10 is a flowchart illustrating the operation of the memory module900 described with reference to FIG. 9.

Referring to FIG. 10, at step S1010, the first volatile memory devices911 to 914 and the second volatile memory devices 921 to 924 maycommunicate with the memory controller 9 of the host. Since the firstvolatile memory devices 911 to 914 and the second volatile memorydevices 921 to 924 share the same control bus CMD/ADDR_BUS, the firstvolatile memory devices 911 to 914 and the second volatile memorydevices 921 to 924 may perform the same operation. However, sinceseparate data buses DATA_BUS3_1 to DATA_BUS3_4 and DATA_BUS4_1 toDATA_BUS4_4 are provided for the respective volatile memory devices 911to 914 and 921 to 924, the memory controller 9 of the host can exchangedifferent data with each of the volatile memory devices 911 to 914 and921 to 924.

At step S1020, a trigger condition may be satisfied. The triggercondition may indicate a condition for backing up the data of the firstvolatile memory devices 911 to 914 and the second volatile memorydevices 921 to 924 into the nonvolatile memory device 930. For example,when a failure of the host power HOST_VDD and HOST_VSS is detected, thefailure detection may satisfy the trigger condition. Alternatively, whena backup operation is performed by a command of the memory controller 9of the host, the backup operation command of the memory controller 9 ofthe host may satisfy the trigger condition.

At step S1030, the control for the first volatile memory devices 911 to914 and the second volatile memory devices 921 to 924 may be switchedfrom the memory controller 9 of the host to the controller 940.Furthermore, the power used by the memory module 900 may be switchedfrom the host power HOST_VDD and HOST_VSS to the emergent power EMG_VDDand EMG_VSS supplied by the emergent power supply unit 10. Furthermore,according to the control of the controller 940, the data buses used bythe first volatile memory devices 911 to 914 may be switched from thethird data buses DATA_BUS3_1 to DATA_BUS3_4 to the first data busDATA_BUS1, and the data buses used by the second volatile memory devices921 to 924 may be switched from the fourth data buses DATA_BUS4_1 toDATA_BUS4_4 to the second data bus DATA_BUS2. Each of the first volatilememory devices 911 to 914 and the second volatile memory devices 921 to924 may include eight data pads DQ0 to DQ7. Among the data pads DQ0 toDQ7, four data pads DQ0 to DQ3 may be coupled to the first data busDATA_BUS1 and the second data bus DATA_BUS2, and the other four datapads DQ4 to DQ7 may be coupled to the third data buses DATA_BUS3_1 toDATA_BUS3_4 and the fourth data buses DATA_BUS4_1 to DATA_BUS4_4. Thedata buses used by the first volatile memory devices 911 to 914 and thesecond volatile memory devices 921 to 924 may be changed in response toa command of the controller 940. The zeroth data pads DQ0 of the firstvolatile memory devices 911 to 914 may be coupled to different datalines of the first data bus DATA_BUS1, and the zeroth data pads DQ0 ofthe second volatile memory devices 921 to 924 may be coupled todifferent data lines of the second data DATA_BUS2. Through thisconfiguration, the first volatile memory devices 911 to 914 mayindividually enter the PDA mode, and the second volatile memory devices921 to 924 may individually enter the PDA mode.

At step S1041, the data of the first volatile memory device 911 and thesecond volatile memory device 921 (hereafter referred to as a firstvolatile memory group) may be backed up into the nonvolatile memorydevice 930. This operation may be performed as follows. First, the CALof the first volatile memory group 911 and 921 may be set to a firstvalue (for example, ‘0’), and the CAL of the other volatile memorydevices 912 to 914 and 922 to 924 may be set to a second value (forexample, ‘3’), which is different from the first value. Then, thecontroller 940 may read data from the first volatile memory group 911and 921 using the CAL of the first value, and store the read data in thenonvolatile memory device 930.

At step S1042, the data of the first volatile memory device 912 and thesecond volatile memory device 922 (hereafter referred to as a secondvolatile memory group) may be backed up into the nonvolatile memorydevice 930. This operation may be performed as follows. First, the CALof the second volatile memory group 912 and 922 may be set to the firstvalue (for example, ‘0’), and the CAL of the other volatile memorydevices 911, 913, and 914 and 921, 923, and 924 may be set to the secondvalue (for example, ‘3’). Then, the controller 940 may read data fromthe second volatile memory group 912 and 922 using the CAL of the firstvalue, and store the read data in the nonvolatile memory device 930.

At step S1043, the data of the first volatile memory device 913 and thesecond volatile memory device 923 (hereafter referred to as a thirdvolatile memory group) may be backed up into the nonvolatile memorydevice 930. This operation may be performed as follows. First, the CALof the third volatile memory group 913 and 923 may be set to the firstvalue (for example, ‘0’), and the CAL of the other volatile memorydevices 911, 912, and 914 and 921, 922, and 924 may be set to the secondvalue (for example, ‘3’). Then, the controller 940 may read data fromthe third volatile memory group 913 and 923 using the CAL of the firstvalue, and store the read data in the nonvolatile memory device 930.

At step S1044, the data of the first volatile memory device 914 and thesecond volatile memory device 924 (hereafter referred to as a fourthvolatile memory group) may be backed up into the nonvolatile memorydevice 930. This operation may be performed as follows. First, the CALof the fourth volatile memory group 914 and 924 may be set to the firstvalue (for example, ‘0’), and the CAL of the other volatile memorydevices 911 to 913 and 921 to 923 may be to the second value (forexample, ‘3’). Then, the controller 940 may read data from the fourthvolatile memory group 914 and 924 using the CAL of the first value, andstore the read data in the nonvolatile memory device 930. The backupoperation may be completed by step S1044.

The method in which the controller 940 sets the CALs of the firstvolatile memory devices 911 to 914 and the second volatile memorydevices 921 to 924 in various manners and accesses only first and secondvolatile memory devices having specific CAL at steps S1041 to S1044 maybe understood with reference to FIGS. 4 to 7. Furthermore, as describedwith reference to FIG. 9, the CAL difference dCAL between the first andsecond values of CAL may be set to satisfy the relation of dCAL≧tRCD anddCAL<tRP.

After the backup operation is completed, a restoration condition may besatisfied at step S1050. The restoration condition may indicate acondition for restoring the data, which is backed up in the nonvolatilememory device 930, to the first volatile memory devices 911 to 914 andthe second volatile memory devices 921 to 924. For example, when thehost power HOST_VDD and HOST_VSS is normally restored, it may satisfythe restoration condition. Alternatively, when the restoration operationis performed in response to a command of the memory controller 9 of thehost, the restoration operation command of the memory controller 9 ofthe host may satisfy the restoration condition. Since the host powerHOST_VDD and HOST_VSS is normally restored, the following restorationoperation may be performed using the host power HOST_VDD and HOST_VSS.

At step S1061, the data of the first volatile memory group 911 and 921may be restored. This operation may be performed as follows. First, theCAL of the first volatile memory group 911 and 921 may be set to a thirdvalue (for example, ‘0’), and the CAL of the other volatile memorydevices 912 to 914 and 922 to 924 may be set to a fourth value (forexample, ‘3’), which is different from the third value. Then, thecontroller 940 may read data from the nonvolatile memory device 930, andwrite the read data to the first volatile memory group 911 and 921.

At step S1062, the data of the second volatile memory group 912 and 922may be restored. This operation may be performed as follows. First, theCAL of the first volatile memory group 912 and 922 may be set to thethird value, and the CAL of the other volatile memory devices 911, 913,and 914 and 921, 923, and 924 may be set to the fourth value. Then, thecontroller 940 may read data from the nonvolatile memory device 930, andwrite the read data to the second volatile memory group 912 and 922.

At step S1063, the data of the third volatile memory group 913 and 923may be restored. This operation may be performed as follows. First, theCAL of the third volatile memory group 913 and 923 may be set to thethird value, and the CAL of the other volatile memory devices 911, 912,and 914 and 921, 922, and 924 may be set to the fourth value. Then, thecontroller 940 may read data from the nonvolatile memory device 930, andwrite the read data to the third volatile memory group 913 and 923.

At step S1064, the data of the fourth volatile memory group 914 and 924may be restored. This operation may be performed as follows. First, theCAL of the fourth volatile memory group 914 and 924 may be set to thethird value, and the CAL of the other volatile memory devices 911 to 913and 921 to 923 may be set to the fourth value. Then, the controller 940may read data from the nonvolatile memory device 930, and write the readdata to the fourth volatile memory group 914 and 924. The restorationoperation may be completed by step S1064.

After the restoration operation is completed, the control for the firstvolatile memory devices 911 to 914 and the second volatile memorydevices 921 to 924 may be switched from the controller 940 to the memorycontroller 9 of the host, at step S1070. Furthermore, the data bus usedby the first volatile memory devices 911 to 914 may be switched from thefirst data bus DATA_BUS1 to the third data buses DATA_BUS3_1 toDATA_BUS3_4, and the data bus used by the second volatile memory devices921 to 924 may be switched from the second data bus DATA_BUS2 to thefourth data buses DATA_BUS4_1 to DATA_BUS4_4.

As described above, the first volatile memory devices 911 to 914 mayshare the control bus CMD/ADDR_BUS and the first data bus DATA_BUS1 forcommunication with the controller 940. However, as the controller 940sets the CAL to different values, the controller 940 may separatelyaccess the first volatile memory devices 911 to 914 in order to back upor restore data. Furthermore, the second volatile memory devices 921 to924 may share the control bus CMD/ADDR_BUS and the second data busDATA_BUS2 for communication with the controller 940. However, as thecontroller 940 sets the CAL to different values, the controller 940 mayseparately access the second volatile memory devices 921 to 924 in orderto back up or restore data.

FIG. 11 is a block diagram illustrating the memory module 900 inaccordance with another embodiment of the present invention.

Referring to FIGS. 9 and 11, the memory module 900 shown in FIG. 11 maybe substantially the same as the memory module 900 described withreference to FIG. 9 except that the memory module shown in FIG. 11 mayfurther include multiplexers 1101 to 1108, and four data pads DQ0 to DQ3may be used in the first volatile memory devices 911 to 914 and thesecond volatile memory devices 921 to 924.

When the first volatile memory devices 911 to 914 communicate with thememory controller 9 of the host, the data pads DQ0 to DQ3 of the firstvolatile memory devices 911 to 914 may be coupled to the third databuses DATA_BUS3_1 to DATA_BUS3_4 by the multiplexers 1101 to 1104. Whenthe first volatile memory devices 911 to 914 communicate with thecontroller 940, the data pads DQ0 to DQ3 of the first volatile memorydevices 911 to 914 may be coupled to the first data bus DATA_BUS1 by themultiplexers 1101 to 1104.

When the second volatile memory devices 921 to 924 communicate with thememory controller 9 of the host, the data pads DQ0 to DQ3 of the secondvolatile memory devices 921 to 924 may be coupled to the fourth databuses DATA_BUS4_1 to DATA_BUS4_4 by the multiplexers 1105 to 1108. Whenthe second volatile memory devices 921 to 924 communicate with thecontroller 940, the data pads DQ0 to DQ3 of the second volatile memorydevices 921 to 924 may be coupled to the second data bus DATA_BUS2 bythe multiplexers 1105 to 1108.

In accordance with the embodiments of the present invention, while thenumber of lines between the controller and the memory devices arereduced, the controller can separately access the memory devices.

Although various embodiments have been described for illustrativepurposes, it will be apparent to those skilled in the art that variouschanges and modifications may be made without departing from the spiritand scope of the invention as defined in the following claims.

What is claimed is:
 1. A memory system comprising: a data bus configuredto transfer data; a control bus configured to transfer a command andaddress including a command address latency (CAL); first and secondmemory devices coupled to the data bus and the control bus; and acontroller configured to control the first and second memory devicesthrough the data bus and the control bus, wherein the first and secondmemory devices have different values of the CAL, and wherein adifference of the CAL values is greater than or equal to a RAS to CASdelay time (tRCD).
 2. The memory system of claim 1, wherein thedifference of the CAL values is smaller than a row precharge time (tRP).3. A memory module comprising: a first data bus configured to transferdata; a control bus configured to transfer a command and addressincluding a command address latency (CAL); a plurality of first volatilememory devices coupled to the first data bus and the control bus; one ormore nonvolatile memory devices; and a controller configured to providethe command and address through the control bus and the first data busto store data of the plurality of first volatile memory devices into thenonvolatile memory devices when a trigger condition is satisfied,wherein when the trigger condition is satisfied, the controller controlsa specific one of the plurality of first volatile memory devices to havethe CAL of a first value, and others of the plurality of first volatilememory devices to have the CAL of a second value.
 4. The memory moduleof claim 3, wherein the command and address include the CAL of the firstvalue when the controller accesses the specific one of the pluralityfirst volatile memory devices.
 5. The memory module of claim 3, furthercomprising: a second data bus configured to transfer data; and aplurality of second nonvolatile memory devices coupled to the seconddata bus and the control bus, wherein the controller further providesthe command and address through the control bus and the second data busto store data of the plurality of second volatile memory devices intothe nonvolatile memory devices, when the trigger condition is satisfied,and wherein when the trigger condition is satisfied, the controllercontrols a specific one of the plurality of second volatile memorydevices to have the CAL of the first value, and others of the pluralityof second volatile memory devices to have the CAL of a second value. 6.The memory module of claim 5, wherein the command and address includethe CAL of the first value when the controller accesses the specific oneof the plurality of second volatile memory devices.
 7. The memory moduleof claim 5, further comprising a plurality of third data buses throughwhich the plurality of first volatile memory devices independentlyperform data communication with a memory controller of a host.
 8. Thememory module of claim 7, further comprising a plurality of fourth databuses through which the plurality of second volatile memory devicesindependently perform data communication with the memory controller ofthe host.
 9. The memory module of claim 3, wherein the second value isgreater than the first value, and a difference between the first andsecond values is greater than or equal to a RAS to CAS delay time(tRCD).
 10. The memory module of claim 9, wherein the difference betweenthe first and second values is smaller than a row precharge time (tRP).11. The memory module of claim 3, further comprising a registerconfigured to transfer a command and address between a memory controllerof a host and the control bus.
 12. An operation method of a memorymodule including first to Nth volatile memory groups, each of the firstto Nth volatile memory groups includes one or more volatile memorydevices, one or more nonvolatile memory devices, and a controller, theoperation method comprising: exchanging data between the first to Nthvolatile memory groups and a memory controller of a host; controlling,by the controller, a specific one of the first to Nth volatile memorygroups to have a command address latency (CAL) of a first value, andothers of the first to Nth volatile memory groups to have the CAL of asecond value when a trigger condition is satisfied; and providing acommand and address including the CAL of the first value to store dataof the specific one of the first to Nth volatile memory groups into thenonvolatile memory devices when the trigger condition is satisfied. 13.The operation method of claim 12, further comprising repeating thecontrolling of the CAL of the first and second values and the providingof the command and address including the CAL of the first value for eachof the first to Nth volatile memory groups.
 14. The operation method ofclaim 12, further comprising: controlling, by the controller, thespecific one of the first to Nth volatile memory groups to have the CALof a third value, and the others of the first to Nth volatile memorygroups to have the CAL of a fourth value when a restoration condition issatisfied; and providing a command and address including the CAL of thethird value to restore data of the nonvolatile memory devices into thespecific one of the first to Nth volatile memory groups when therestoration condition is satisfied.
 15. The operation method of claim14, further comprising repeating the controlling of the CAL of the thirdand fourth values and the providing of the command and address includingthe CAL of the third value for each of the first to Nth volatile memorygroups.
 16. The operation method of claim 14, wherein the fourth valueis greater than the third value, and a difference between the third andfourth values is greater than or equal to a RAS to CAS delay time(tRCD).
 17. The operation method of claim 16, wherein the differencebetween the third and fourth values is smaller than a row precharge time(tRP).
 18. The operation method of claim 12, wherein the second value isgreater than the first value, and a difference between the first andsecond values is greater than or equal to a RAS to CAS delay time(tRCD).
 19. The operation method of claim 18, wherein the differencebetween the first and second values is smaller than a row precharge time(tRP).